A lobby group pushing to change Australia's flag predicts it will be successful within five to 10 years.

AusFlag's campaign to remove the Union Jack is backed by prominent Australians including journalist Ray Martin and footballer Ron Barassi.

"I object to having the British flag in the corner of our flag," Martin told the Herald Sun newspaper.

"We have well and truly reached the point where we should have our own flag. I think we have to grow up and move on to the next stage."

AusFlag spokesman Harold Scruby predicts Australians will soon vote to become a republic and are likely to want a new flag as well.

He says Australians should take note of Canada's decision to change its flag.

"The Canadian flag has been so successful in uniting the Indigenous people, the French, the British, every other group that has come there that I know that we can do a lot better," he said.

The Greens Leader Bob Brown says he supports the move to change the Australian flag.

Senator Brown says the Union Jack is a symbol of the British empire and has little meaning for Australians with links to countries other than Great Britain.

"The Government ought to be asking Australians about what to put there," he said.

"But a symbol of Indigenous heritage or of Australia's own view of itself as a nation in that corner may be something reflecting the Australian colours of green and gold.

"When we put an Australian symbol rather than the symbol of another country in the top left hand corner of the flag we will have an Australian flag."

But both major political parties have rebuffed the campaign.

The Deputy Prime Minister, Julia Gillard, told Sky News the flag should stay the same and that Australians identify with it.

"It's part of our history. I believe it should be part of our future," she said.

"It's become our flag, our national symbol."

The Opposition Leader, Tony Abbott, says most Australians agree and says there is no reason to change the flag.

"I think that the Australian flag is more popular than ever," he said.

"It represents our history and our hopes and I think people want to keep it."

The Victorian Premier, John Brumby, supports the retention of the current design, but says he is open to a community debate on the issue.

However, he says it would be a complicated and frustrating process.

"If you look through the Canadian experience, it took years and years and years and years, and at the end of the day there was really no community consensus," he said.

"Because even if you said 'oh yeah, let's change it', you wouldn't get a community consensus about what a new flag should be."

Meanwhile, Tasmanian Aborigines have welcomed moves to change the Australian flag, but it comes with conditions.

The Tasmanian Aboriginal Centre's Michael Mansell says a new Australian flag could incorporate the aboriginal flag, but only if a new treaty was signed.

"If there was return of land, Aboriginal people got self-determination and an economic base, and the flag was then changed to incorporate the Aboriginal flag, that new flag would symbolise an agreement reached after 200 years and would herald a basis for better relations into the future," he said.